Problem: $ E = \left[\begin{array}{rrr}1 & 2 & 1 \\ 1 & 1 & 0 \\ 0 & 0 & 2\end{array}\right]$ What is $ E^{-1}$ ?
$ = \left[\begin{array}{rrr}-1 & 2 & \frac{1}{2} \\ 1 & -1 & -\frac{1}{2} \\ 0 & 0 & \frac{1}{2}\end{array}\right]$